1. Field of the Invention
The present invention relates to an artificial respiration apparatus that forcibly supplies air to a patient who cannot breathe by himself/herself and that can operate so as to reduce the load on the patient when the patient spontaneously starts breathing.
2. Description of the Related Art
FIG. 5 shows a configuration of a conventional artificial respiration apparatus. Hereinafter, explanation will be given on the conventional artificial respiration apparatus with reference to FIG. 5.
The conventional respiration apparatus 50 includes: a blower 52 for simultaneously generating a positive pressure Ap and a negative pressure An; a rotary valve mechanism 54 for alternately selecting the positive pressure Ap and the negative pressure An generated by the blower 52 and converting the positive and negative pressures into an oscillating air pressure Apn; and a diaphragm block 56 which is urged by the oscillating air pressure Apn from the rotary valve mechanism 54, so as to supply air to a patient P. Moreover, the artificial respiration apparatus 50 includes: a diaphragm neutral position controller 60 for maintaining a neutral position of a diaphragm 561 of the diaphragm block 56; and a respiration gas port 62 for introducing the respiration gas.
The blower 52 has a positive pressure pipe 521 and a negative pressure pipe 522, so that air is supplied to the blower 52 through the negative pressure pipe 522 and discharges the air through the positive pressure pipe 521. The negative pressure pipe 522 is connected to an orifice pipe 523 communicating with the open air. The positive pressure pipe 521 is connected to an orifice pipe 524 communicating with the open air.
The rotary valve mechanism 54 is constituted by a rotary valve 544 having ports 541, 542, 543, and a drive block 545 for rotating the rotary valve 544. The drive block 545 includes a motor and a reduction gear (not depicted) so as to rotate the rotary valve 544 at 900 rpm for example. While the rotary valve 544 makes a single turn, the port 541 and the port 542 are successively made to communicate with the port 543. The port 543 is connected to an oscillating air pressure pipe 546 for transmitting the oscillating air pressure Apn to the diaphragm block 56. A flow control valve 547 is inserted into the oscillating air pressure pipe 546.
The diaphragm block 56 includes a diaphragm 561 formed by an expandable member serving as a partition between a pressurizing chamber 562 and a pressurized chamber 563. The pressurizing chamber 562 is connected to the oscillating air pressure pipe 546.
The respiration gas port 62 is constituted by a blender 621 for mixing the open air with oxygen prepared in advance; and a humidifier 622 for humidifying the gas to be sent out from the blender 521. The humidifier 622 is connected to a respiration gas pipe 623 for supplying to the patient P the respiration gas Ai which has passed through the humidifier. The respiration gas pipe 623 communicates with the pressurized chamber 563 and has a pressure sensor 624 provided in the vicinity of the patient P.
The diaphragm neutral position controller 60 includes: a diaphragm position sensor 601 for detecting a position of the diaphragm 561 of the diaphragm block 56; a pressure regulating valve 64 for controlling the positive pressure Ap, the negative pressure An, or the oscillating air pressure Apn; a control block 66 for controlling the pressure regulating valve 64 according to the position of the diaphragm 561 detected by the diaphragm position sensor 601.
The pressure regulating valve 64 has a configuration similar to a rotary valve and is constituted by a main body 646 having ports 641 to 645 and an actuator 647 for rotating a part of the main body in normal and reverse directions. The actuator 647 is constituted by a motor and a reduction gear (not depicted) and can rotate a part of the main body 646 by a desired angle. The control block 66 is, for example, a microcomputer including a CPU, ROM, RAM, I/O interface, and the like.
In the artificial respiration apparatus 50, the single blower 52 serves to generate both of the positive pressure and the negative pressure. That is, the blower 52 has a large load. On the other hand, in order to increase the ventilation amount of the artificial respiration apparatus 50, it is most effective to increase the power of the blower 52. However, if the power is to be increased with the single blower 52, it becomes necessary to design a special blower having very large dimensions and weight. Such a blower is not available on market and should be prepared by a special order.
This has been preventing reduction in size and weight as well as cost of the conventional artificial respiration apparatus 50. Moreover, such a large blower 52 requires a 200 V power source or a large current receptacle even if a 100 V power source can be used. This makes it difficult to use the artificial respiration apparatus 50 even in a small hospital.
Next, explanation will be given on the reason why the blower 52 of the artificial respiration apparatus 50 should have such a large load. A "blower" is an apparatus constituted by a motor and a fan for sucking air from the suction side and discharging the air from the discharge side. The blower 52 generates a negative pressure An by sucking air from the suction side and generates a positive pressure Ap by discharging the sucked air from the discharge side.
Here, for use of the positive pressure Ap, the rotary valve mechanism 54 makes the discharge side of the blower 52 communicate with the oscillating air pressure pipe 546 while closing the suction side of the blower 52. Here, if the suction side is closed completely, it becomes impossible to obtain air for discharge. Accordingly, the suction side is connected to the orifice pipe 523 communicating with the open air.
On the contrary, when using the negative pressure An, the rotary valve mechanism 54 makes the discharge side of the blower 52 closed and the suction side of the blower 52 communicate with the oscillating air pressure pipe 546. Here, if the discharge side is closed completely, the sucked air cannot be discharged. Accordingly, the discharge side is also connected to an orifice pipe 524 communicating with the open air.
Accordingly, when using the positive air Ap, the suction side takes in air via the orifice pipe 523, whereas the discharge side discharges the air via the oscillating air pressure pipe 546 and simultaneously with this, the air leaks out via the orifice pipe 524. On the contrary, when using the negative pressure An, the discharge side discharges air via the orifice pipe 524, whereas the suction side sucks air via the oscillating air pressure pipe 546 and simultaneously with this, air flows in via the orifice pipe 523. Thus, operation of the artificial respiration apparatus 50 is inevitably accompanied by useless air leak out and flow in. This significantly increases the load of the blower 52.